Add support for config tunables

[Vladimir Grevtsev]

Classic charms (nova-cloud-controller, neutron-api etc) have a "config-flags" option. This option would be useful in the masakari-monitors (and
other reactive charms).

config-flags
(string) Comma-separated list of key=value config flags. These values will be placed in the nova.conf [DEFAULT] section.

(gnuoy: I have removed references to the masakari process monitor as that is not supported by the charm and there is no intention to add it. This bug is about adding config-flags config option)

[James Page (james-page)]

as a side note - the options referenced relate to process monitoring which is a part of Masakari that the charms project does not enable.

[Zeeshan Ali Shah (babal1nux)]

Thanks James , please advice me if that is ok

1) i have created config.yaml in charmed masakri monitor
2) now creating @when config changed kind of methods to be called in case config changed
3) how do i actually set the values in masakri itself ? which class should i use ? or any other way to set these values in masakri ?

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/charm-masakari-monitors/+/836011
Committed: https://opendev.org/openstack/charm-masakari-monitors/commit/01679e56a35c6de4977b17f7d792181bab2baafb
Submitter: "Zuul (22348)"
Branch: master

commit 01679e56a35c6de4977b17f7d792181bab2baafb
Author: Zeeshan Ali Shah <email address hidden>
Date: Thu Mar 31 13:05:59 2022 +0500

    Enable multiple arbitrary config-flags

    The config flags are a comma-seperated list of keys and values.
    This enables an operator to pass arbitrary configuration into
    the masakari-monitors configuration.

    Closes-Bug: #1941650
    Change-Id: I3571bf7dfcb092ce5d04f439806e9a25465e16c5